Positive resist composition

ABSTRACT

Disclosed is an improved, chemically-amplifying positive resist composition for radiations, especially UV rays, deep-UV rays, excimer laser beams, X-rays, electron beams. The composition comprises (A) a resin component whose solubility in an alkaline aqueous solution is increased by the action of acids, (B) a compound which generates an acid when exposed to radiations, and (A) a resin component, (B) an acid-generating agent and (C) an organic carboxylic acid compound, in which said resin component (A) is a mixture comprising (a) a polyhydroxystyrene where from 10 to 60 mol % of the hydroxyl groups have been substituted by residues of a general formula (I): ##STR1## wherein R 1  represents a hydrogen atom or a methyl group, R 2  represents a methyl group or an ethyl group, and R 3  represents a lower alkyl group having 1 to 4 carbon atoms; 
     and (b) a polyhydroxystyrene where from 10 to 60 mol % of the hydroxyl groups have been substituted by tert-butoxy-carbonyloxy groups. The composition has a high sensitivity, a high resolution, high heat resistance, good width characteristic in focus depth and good post-exposure storage stability, has good storage stability as a resist solution, and gives resist patterns with good profiles, without depending on the substrate to which it is applied. The composition is useful for forming fine patterns in producing ultra-LSIs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/625,931 filed Apr. 1,1996, now U.S. Pat. No. 5,736,296, which is a merger of and is acontinuation-in-part of U.S. application Ser. No. 08/422,950 filed Apr.17, 1997 now abandoned, and a continuation-in-part of U.S. ApplicationSer. No. 08/498,185 filed Jul. 5, 1995 now abandoned, which is acontinuation-in-part of U.S. Application Ser. No. 08/422,950 filed Apr.17, 1995, now abandoned all of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a positive resist composition and, moreprecisely, to a chemically-amplifying positive resist compositionsensitive to UV rays, deep-UV rays, excimer laser beams(such as KrFlaser, ArF laser, etc.), X-rays, electron beams, etc., which has a highsensitivity, a high resolution, high heat resistance, good widthcharacteristic in focus depth and good post-exposure storage stability,has good storage stability as a resist solution, and gives resistpatterns with good profiles on substrates without depending onsubstrates to which it is applied.

BACKGROUND OF THE INVENTION

Semiconductor devices such as ICs, LSIs, etc, have heretofore beenproduced by repeating several times a series of processes comprisingphotolithography using photoresist compositions, etching, diffusion ofimpurities and wiring. Concretely, in the photolithographic process, athin film of a photoresist composition is formed on a silicon wafer bymeans of, for example, spin coating, the resultant is exposed to activerays such as UV rays, etc., via a mask pattern for a semiconductordevice, and then developed to give a resist pattern, and thereafter thesilicon wafer thus having thereon the resist pattern acting as aprotective film is etched. As the photoresist composition preferablyused in the photo-lithography, there has been known a positivephotoresist composition comprising, as basic components, analkali-soluble novolak resin and a quinonediazido group-containingcompound for which a resolution on the order of sub-microns(1 μm orless) or still half-microns(0.5 μm or less) is required and which usesUV rays such as g-line(436 nm) and i-line(365 nm) for exposure.

Recently, larger scale integrations in semiconductor devices are desiredincreasingly, requiring ultra-fine patterning on the order of quartermicrons(0.25 μm or less) in the mass production of ultra-LSIs, etc.However, the conventional positive photoresist composition comprising,as basic components, an alkali-soluble novolak resin and aquinonediazido group-containing compound hardly gives such an ultra-finepatterning as mentioned above. Therefore, it has been demanded todevelop a resist using deep-UV rays of shorter wavelength (200-300 nm),excimer laser beams such as KrF laser and ArF laser, electron beams andX-ray. At present, a chemically-amplifying resists which can achieve ahigh resolution, use the catalytic and chain reactions of the acid to begenerated by exposure to radiations, have a quantum yield of 1 or more,and can achieve a high sensitivity, have been of interest and developedintensively.

As one example of such chemically-amplifying positive resists, there isknown a resist comprising a resin component derived frompolyhydroxystyrene by substituting its hydroxyl groups bytert-butoxycarbonyloxy groups or the like and an acid-generating agentof an onium salt or the like (U.S. Pat. No. 4,491,628).

However, the above-mentioned, known chemically-amplifying positiveresist was not satisfactory in practical use, since the resolution andthe width characteristic in focus depth are not satisfactory, and sinceit may cause a problem so-called bridging that the crosssectionalprofile of the patterns to be made of the resist is often broadenedupward like eaves. Concretely, when the chemically-amplifying positiveresist coated on a substrate are exposed, stored for a while and thendeveloped to give patterns, the patterns cannot have good profiles sincethe acids generated by the exposure are inactivated while the exposedresist films are stored. (which phenomenon is referred to as decrease in"post-exposure storage stability" of the positive resist, here-inafter)

The problem of post-exposure storage stability is peculiar tochemically-amplifying positive resists. When the bridging occurs, adesired wiring pattern cannot be given, which is a serious problem forthe production of semiconductor devices. For the purpose of improvingthe post-exposure storage stability, there has been proposed a method inwhich a top coating layer is provided on a resist layer, whereby theinactivation of the acids generated by the exposure is prevented. Inthis method, however, the production steps are increased, which leadsthe decrease in throughput and high production cost as well. From thesereasons, this method is unfavorable. Accordingly, there has beenstrongly demanded to develop a resist having good post-exposure storagestability without providing a top coating layer.

The above-mentioned chemically-amplifying positive resist has anotherproblem that it characteristically depended on substrates to which theyare applied, and some of them, when applied on an unsuitable substratesuch as a substrate coated with an insulating film such as siliconnitride (SiN), boron-phosphorus-silicate glass (BPSG) or the like filmor on a substrate coated with titanium nitride (TiN), often formedresist patterns with poor profiles expanding downward to the substrates(which is referred to as "substrate dependency", hereinafter). It hasbeen assumed that the acids generated by the exposure are inactivated bythe action of amines remaining around the substrate in the filmformation step, which causes the formation of resist patterns with poorprofiles expanding downward to the substrates.

Moreover, when such resist is coated on a substrate coated with ametallic film such as an aluminum-silicon-copper (Al--Si--Cu) alloy filmand a tungsten (W) film, the resist pattern formed is influenced bystanding waves and the crosssectional profile of the resist pattern iswaved. For the purpose of solving the problems of such substratedependency and influence by standing waves, there has been proposed amethod in which an anti-reflection coating layer is provided between thesubstrate and the resist layer. In this method, however, the productionsteps are increased, which leads the decrease in throughput and highproduction cost as well. From these reasons, this method is alsounfavorable. Accordingly, there has been strongly demanded to develop aresist without an anti-reflection coating layer which can give resistpatterns with good profile not depending on substrates to which it isapplied and hardly influenced by standing waves.

In addition to the above-mentioned problems, the conventional resistcompositions have still another problem. That is, when the resistcompositions are prepared in solutions, they have such a poor storagestability that the solutions often generate solid substances while thesolutions are stored. Accordingly, there has also been demanded todevelop a resist composition capable of giving a resist solution whichhas a good storage stability and does not generate any solid substancesduring it is stored.

In these situations, we, the present inventors have assiduously studiedso as to develop chemically-amplifying positive resist compositions freefrom the above-mentioned problems and, as a result, have found that byusing, as a resin component whose solubility in an alkaline aqueoussolution is increased by the action of acids, a mixture of two differentpolyhydroxystyrenes where the hydroxyl groups have been substituted bytwo different kinds of substituents in certain degrees, respectively,and also a mixture of the preceeding two different polyhydroxystyrenesand an organic carboxylic acid, it becomes possible to provide achemically-amplifying positive resist composition sensitive toradiations such as UV rays, deep-UV rays, excimer laser beams (such asKrF laser, ArF laser, etc.), X-rays, electron beams, etc., which has ahigh sensitivity, a high resolution, high heat resistance, good widthcharacteristic in focus depth and good post-exposure storage stability,has good storage stability when it is prepared in a resist solution, andgives resist patterns with good profiles on substrates without dependingon substrates to which it is applied. On the basis of these findings, wehave completed the present invention.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a positive resistcomposition which is sensitive to radiations, especially deep-UV raysand excimer laser beams (such as KrF laser, ArF laser, etc.) and whichhas a high sensitivity, a high resolution, high heat resistance, goodwidth characteristic in focus depth and good post-exposure storagestability and, furthermore, which has good storage stability when it isprepared in a resist solution.

Another object of the present invention is to provide a positive resistcomposition capable of forming resist patterns with good profiles,without depending on substrates to which it is applied.

The above-mentioned positive resist composition according to the presentinvention has a high sensitivity, a high resolution on the order ofquarter microns or less, high heat resistance, good width characteristicin focus depth and good post-exposure storage stability. Furthermore,the composition is capable of forming resist patterns with goodprofiles, without depending on substrates to which it is applied.Therefore, the composition of the present invention is satisfactorilyapplicable to the process for producing semiconductor devices for whicha resolution on the order of quarter microns is required. Moreover, thecomposition of the present invention has superior resistcharacteristics, compared to the resist composition mentioned above as aconventional one which comprising a resin component where the hydroxylgroups have been substituted by tert-butoxy-carbonyloxy groups and anacid-generating agent. Therefore, the composition of the presentinvention is applicable to production of a semiconductor device in whichthe composition is coated on a substrate in a single layer withoutproviding a top coat layer or an anti-reflecting coat layer whichincrease the steps for producing the device, by which the device can beproduced at low cost and quite effectively. From these reasons, thecomposition of the present invention is satisfactory in practical use.

DETAILED DESCRIPTION OF THE INVENTION

The present invention attains the above-mentioned objects, providing apositive resist composition comprising (A) a resin component whosesolubility in an alkaline aqueous solution is increased by the action ofacids (Such a resin component is hereinafter simply referred to as "aresin component"), and (B) a compound which generates an acid whenexposed to radiations (Such a compound is hereinafter referred to as "anacid-generating agent"), in which the resin component (A) is a mixturecomprising from 30 to 90% by weight of (a) a polyhydroxystyrene wherefrom 10 to 60 mol % of the hydroxyl groups have been substituted byresidues of a general formula (I): ##STR2## wherein R¹ represents ahydrogen atom or a methyl group, R² represents a methyl group or anethyl group, and R³ represents a lower alkyl group having 1 to 4 carbonatoms;

and from 10 to 70% by weight of (b) a polyhydroxystyrene where from 10to 60 mol % of the hydroxyl groups have been substituted bytert-butoxycarbonyloxy groups, and also a positive resist compositioncomprising (A) a resin component, (B) an acid-generating agent and (C)an organic carboxylic acid compound.

As mentioned above, the positive resist composition of the presentinvention contains the component (A) of a mixture of the components (a)and (b). Therefore, the composition never cause such a decrease ineither heat resistance or resolution of the resist patterns to be formedthat a resist composition containing, as the component (A), apolyhydroxystyrene where the hydroxyl groups have partly beensubstituted by alkoxyalkoxy groups of a general formula (I) or apolyhydroxystyrene where the hydroxyl groups have partly beensubstituted by tert-butoxycarbonyloxy groups as a single component mayoccur. Furthermore, the composition of the present invention has a highsensitivity, a high resolution, high heat resistance, good widthcharacteristic in focus depth and good post-exposure storage stability,has good storage stability when it is prepared in a resist solution, andgives resist patterns with good profiles on substrates without dependingon substrates to which it is applied.

In the mixture as the resin component (A), component (a) is from 30 to90% by weight and component (b) is from 10 to 70% by weight based on thetotal weight of compent (A). In this, preferably, component (a) is from50 to 80% by weight and component (b) is from 20 to 50% by weight basedon the total weight of compent (A). Concretely mentioned, as specificexamples of the residues of the general formula (I) in the component(a), are 1-methoxyethoxy group, 1-ethoxyethoxy group, 1-n-propoxy-ethoxygroup, 1-iso-propoxyethoxy group, 1-n-butoxyethoxy group,1-iso-butoxyethoxy group, 1-(1,1-di-methylethoxy)-1-methylethoxy group,1-methoxy-1-methyl-ethoxy group, 1-ethoxy-1-methyl-ethoxy group,1-n-propoxy-1-methylethoxy group, 1-isobutoxy-1-methylethoxy group,1-methoxy-n-propoxy group, and 1-ethoxy-n-propoxy group. Among these,especially preferred are 1-ethoxy-ethoxy group and 1-methoxy-n-propoxygroup, since the sensitivity and the resolution of the positive resistcomposition containing the resin component are well balanced andimproved.

In the positive resist composition of the present invention, the acid tobe generated by the acid-generating agent partly decomposes thetert-butoxycarbonyloxy groups and the residues of formula (I), by whichthe solubility of the resin component (A) in an alkali aqueous solutionon the exposed regions of the film and the dissolution-inhibitingability thereof on the unexposed regions of the film are well balanced,resulting in that the positive resist composition has a highsensitivity, a high resolution and high heat resistance, as well asimproved width characteristic in focus depth.

The above-mentioned component (a) is a polyhydroxystyrene in which thehydroxyl groups have been partly substituted by the residues of formula(I) above, for example, by a known substitution reaction between anunsubstituted polyhydroxystyrene and 1-chloro-1-ethoxy-ethane,1-chloro-1-methoxypropane or the like. In this, the degree ofsubstitution of the hydroxyl groups with such residues is from 10 to 60mol %, preferably from 20 to 50 mol %. If the degree of substitution isless than 10 mol %, the positive resist composition containing the resincomponent cannot give resist patterns with good profiles. If, however,it is more than 60 mol %, the sensitivity of the composition is lowered.Therefore, the degree of substitution not falling within the definedrange is unfavorable. In practical use of the composition, the degree ofsubstitution is preferably from 20 to 50 mol %.

The above-mentioned component (b) is a polyhydroxystyrene in which thehydroxyl groups have been partly substituted by tert-butoxycarbonyloxygroups, for example, by a known substitution reaction between anunsubstituted polyhydroxystyrene and di-tert-butyl-di-carbonate or thelike. In this, the degree of substitution of the hydroxyl groups withtert-butoxycarbonyloxy groups is from 10 to 60 mol %, preferably from 20to 50 mol %. If the degree of substitution is less than 10 mol %, thepositive resist composition containing the resin component cannot giveresist patterns with good profiles. If, however, it is more than 60 mol%, the sensitivity of the composition is lowered. Therefore, the degreeof substitution not falling within the defined range is unfavorable. Inpractical use of the composition, the degree of substitution ispreferably from 20 to 50 mol %.

Each of the above-mentioned resin component shall have a weight-averagemolecular weight falling within the range between 3,000 and 30,000,preferably form 8,000 to 22,000, measured by gel permeationchromatography (GPC) based on polystyrene. If the weight-averagemolecular weight is less than the defined range, the coatability of thecomposition containing the resin is poor. If, however, it is more thanthe same, the solubility of the resin in an aqueous alkaline solution islowered. And the resin components of the present invention shall have amolecular weight distribution (M_(w) /M_(n)), which is defined as aratio between a weight-average molecular weight and a number-averagemolecular weight, falling within the range between 3 to 5.

As the above-mentioned resin component (A), is mentioned only a mixturecomprising two kinds of polyhydroxystyrenes where the hydroxyl groupshave been substituted by the alkoxyalkoxy groups of formula (I) andtert-butoxy-carbonyloxy groups respectively. However, the resincomponent (A) to be in the composition of the present invention is notspecifically limited to the above-mentioned resin component, and may bea mixture comprising two or more kinds of polyhydroxystyrenes where thehydroxyl groups have been substituted by any known acid-releasablesubstituents such as tetrahydropyranyloxy groups, tetrahydrofuranyloxygroups, trimethylsilyloxy groups and the like, respectively.

The acid-generating agent to be in the composition of the presentinvention is not specifically defined but may be any knownacid-generating agent. Concretely mentioned, as the agent, are (i)bissulfonyldiazomethanes such as bis(p-toluenesulfonyl)diazomethane,methylsulfonyl-p-toluene-sulfonyldiazomethane,1-cyclohexylsulfonyl-1-(1,1-dimethyl-ethylsulfonyl)diazomethane,bis(1,1-dimethyl-ethylsulfonyl) diazomethane,bis(1-methylethylsulfonyl)diazomethane,bis-(cyclohexylsulfonyl)diazomethane,bis(2,4-dimethylphenyl-sulfonyl)diazomethane,bis-(4-ethylphenylsulfonyl)diazo-methane,bis(3-methylphenylsulfonyl)diazomethane,bis(4-methoxyphenylsufonyl)diazomethane,bis(4-fluorophenyl-sulfonyl)diazomethane,bis(4-chloro-phenylsulfonyl)diazo-methane, andbis(4-tert-butylphenylsulfonyl)diazomethane; (ii) sulfonylcarbonylalkanes such as 2-methyl-2-(p-toluene-sulfonyl)propiophenone,2-(cyclo-hexyl-carbonyl)-2-(p-toluene sulfonyl)propane,2-methanesulfonyl-2-methyl-(4-methylthio) propiophenone, and2,4-dimethyl-2-(p-toluenesulfonyl)pentane-3-one; (iii) sulfonylcarbonyldiazomethanes such as1-p-toluenesulfonyl-1-cyclohexylcarbonyldiazomethane,1-diazo-1-methylsulfonyl-4-phenyl-2-butanone,1-cyclohexyl-sulfonyl-1-cyclohexylcarbonyldiazomethane,1-diazo-1-cyclohexylsulfonyl-3,3-di-methyl-2-butanone,1-diazo-1-(1,1-di-methylethyl sulfonyl)-3,3-di-methyl-2-butanone,1-acetyl-1-(1-methylethyl sulfonyl)diazomethane,1-diazo-1-(p-toluenesulfonyl)-3,3- di-methyl-2-butanone,1-diazo-1-benzenesulfonyl-3,3-di-methyl-2-butanone, 1-diazo-1-(p-toluenesulfonyl)-3-methyl-2-butanone,2-diazo-2-(p-toluenesulfonyl)cyclohexylacetate, 2-diazo-2-ben-zenesulfonyl tert-butyl acetate, 2-diazo-2-methanesulfonyl iso-propylacetate, 2-diazo-2-benzenesulfonyl cyclohexyl acetate, and2-diazo-2-(p-toluenesulfonyl)tert-butyl acetate; (iv) nitrobenzylderivatives such as 2-nitrobenzyl-p-toluene-sulfonate,2,6-dinitrobenzyl-p-toluenesulfonate, and2,4-di-nitrobenzyl-p-trifluoro-methylbenzenesulfonate; and (v) esters ofpolyhydroxy compounds and aliphatic or aromatic sulfonic acids such aspyrogallic methane sulfonate ester (pyrogallol trimesylate), pyrogallicbenzene sulfonate ester, pyrogallic p-toluene sulfonate ester,pyrogallic p-methoxy benzene sulfonate ester, pyrogallic mesitylenesulfonate ester, pyrogallic benzylsulfonate ester, alkyl gallic acidmethane sulfonate ester, alkyl gallic acid benzene sulfonate ester,alkyl gallic acid p-toluene sulfonate ester, alkyl gallic acid p-methoxybenzene sulfonate ester, alkyl gallic acid mesitylene sulfonate ester,and alkyl gallic acid benzylsulfonate ester. Preferred are the alkylgroup in the afore-mentioned alkyl gallic acid where the alkyl group hasfrom 1 to 15 carbon atoms, and especially octyl group or lauryl group.(vi) onium salt-based acid-generating agents to be in a general formula(II) and (III), and (vii) benzoin tosylate-based acid-generating agentsto be in a general formula (IV) may be used. A general formula (II);

    R.sup.4 --I.sup.+ --R.sup.5 X.sup.-                        (II)

where R⁴ and R⁵ are aryl groups or aryl groups having a substituent andmay be respectively identical or different; X⁻ is any of AsF₆ ⁻, SbF₆ ⁻,PF₆ ⁻, BF₄ ⁻, or CF₃ SO₃ ⁻.

and a general formula (III); ##STR3## where R⁶, R⁷, and R⁸ are arylgroups or aryl groups having a substituent and may be respectivelyidentical or different; X⁻ is any of AsF₆ ⁻, SbF₆ ⁻, PF₆ ⁻ BF₄ ⁻, or CF₃SO₃ ⁻.

A general formula (IV); ##STR4## where R⁹ and R¹⁰ are aryl groups oraryl groups having a substituent and may be identical or different; R¹¹and R¹² are hydrogen atoms, lower alkyl groups, hydroxyl groups, or arylgroups and may be identical or different. n is 0 or 1.

The following are offered as specific onium salts presented by generalformulas (II) and (III). ##STR5##

Among these onium salts, onium salts where trifluoromethanesulfonateforms a negative ion are favorable in that they do not containphosphorous, boron, antimony, or other atoms used as dispersing agentsduring semiconductor element manufacturing.

(vii) The following compounds are offered as specific benzointosylate-based acid-forming agents. ##STR6##

One of these acid-forming agents may be used, or two or more may be usedin combination. Among these, as the acid-generating agents to be in theresists for excimer laser beams, preferred are bissulfonyldiazomethanes, especially bis(cyclohexylsulfonyl)diazomethane,bis(2,4-dimethylphenyl-sulfonyl)diazomethane and their mixture.Particularly, the mixture is preferred since the composition containingthe mixture has high sensitivity.

As the acid-generating agents to be in the resists for electron beams,other acid-generating agents than the above-mentioned (i) and (iii) canbe employed. Especially preferred are nitrobenzyl derivatives of (iv),particularly 2,6-di-nitrobenzyl-p-toluenesulfonate; esters ofpolyhydroxy compounds and aliphatic or aromatic sulfonic acids of (V),particularly pyrogallol trimesylate; onium salts of (vi), particularlybis(p-tert-butylphenyl)iodonium trifluoromethanesulfonate,triphenyl-sulfonium trifluoromethanesulfonate; and (vii) benzointosylate type acid-generating agents.

The proportion of the above-mentioned acid-generating agent to be in thecomposition of the present invention may be from 1 to 20 parts byweight, preferably from 2 to 10 parts by weight, relative to 100 partsby weight of the resin component in the composition. If the proportionof the acid-generating agent is less than 1 part by weight, the agentinsufficiently exhibits its effect. If, however, it is more than 20parts by weight, such too much amount of the agent cannot be completelydissolved in a solvent and, in addition, the miscibility of the agentwith the resin component is lowered.

An organic carboxylic acid compound may be added to the resistcomposition of the present invention, and the composition containing ithas a high sensitivity, a high resolution, good width characteristic infocus depth, and gives resist patterns with good profiles. Inparticular, the composition containing an organic carboxylic acidcompound has good post-exposure storage stability, while giving resistpatterns with good profiles on various substrates.

The organic carboxylic acid compound to be in the composition of thepresent invention is not specifically defined but may be any ofsaturated or unsaturated aliphatic carboxylic acids, alicycliccarboxylic acids, hydroxy-carboxylic acids, alkoxy-carboxylic acids,keto-carboxylic acids, aromatic carboxylic acids, etc. For example, theacid compound includes aliphatic mono- or polycarboxylic acids such asformic acid, acetic acid, propionic acid, butyric acid, isobutyric acid,oxalic acid, malonic acid, succinic acid, glutaric acid, and adipicacid; alicyclic carboxylic acids such as 1,1-cyclo-hexanedicarboxylicacid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylicacid, 1-4-cyclohexanedicarboxylic acid, and 1,1-cyclohexyldiacetic acid;unsaturated aliphatic carboxylic acids such as acrylic acid, crotonicacid, isocrotonic acid, 3-butenoic acid, methacrylic acid, 4-pentenoicacid, propiolic acid, 2-butynoic acid, maleic acid, fumaric acid, andacetylenecarboxylic acid; hydroxycarboxylic acids such as hydroxyaceticacid; alkoxy-carboxylic acids such as methoxyacetic acid andethoxyacetic acid; keto-carboxylic acids such as pyruvic acid; andaromatic carboxylic acid compounds described by a general formula (V)##STR7## wherein R⁻⁻ and R¹⁴ each independently represent a hydrogenatom, a hydroxyl group, a nitro group, a carboxyl group or a vinylgroup, provided that both R¹³ and R¹⁴ should not be hydrogen atoms.

or those of a general formula (VI): ##STR8## wherein n represents 0 oran integer of from 1 to 10. etc

Of these, especially preferred are alicyclic-carboxylic acid compounds,unsaturated aliphatic carboxylic acid compounds and aromatic carboxylicacid compounds.

As examples of the aromatic carboxylic acid compounds of formula (V),mentioned are p-hydroxybenzoic acid, o-hydroxybenzoic acid,2-hydroxy-3-nitrobenzoic acid, 3,5-di-nitrobenzoic acid, 2-nitrobenzoicacid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid,2,6-di-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid,3,5-di-hydroxybenzoic acid, 2-vinylbenzoic acid, 4-vinylbenzoic acid,phthalic acid, terephthalic acid, and iso-phthalic acid, etc. Especiallypreferred are benzoic acids having an o-positioned substituent, such aso-hydroxybenzoic acid, 2-nitrobenzoic acid and phthalic acid, etc.

The aromatic carboxylic acid compounds of formula (VI) can be usedeither as a single compound where n is a singular number or as acombination of two or more different compounds. In practical use, thecomposition of the present invention preferably contains, as the acidcompound, SAX (trade name, produced by Mitsui Toatsu Chemical Co.) whichis sold as a phenolic compound.

One or more of the above-mentioned aromatic carboxylic acid compounds offormula (V) and (VI) above can be in the composition of the presentinvention. The composition of the present invention containing any ofthese aromatic carboxylic acid compounds gives resist patterns with goodprofiles. In addition, the composition has good post-exposure storagestability and therefore always gives resist patterns with good profileswithout depending on the period of time needed after the exposure of thecomposition and before the heating treatment thereof. In particular, thearomatic carboxylic acid compounds of formula (VI) are preferred, sincethe composition of the present invention containing any of them givesresist patterns with true rectangular profiles.

The proportion of the above-mentioned organic carboxylic acid compoundto be in the composition of the present invention may be from 0.01 to 1%by weight, preferably from 0.05 to 0.5% by weight, more preferably from0.07 to 0.3% by weight, relative to the sum of the resin component andthe acid-generating agent to be in the composition. If the proportion ofthe organic carboxylic acid compound is less than 0.01% by weight, thecomposition cannot give resist patterns with good profiles. If, however,it is more than 1% by weight, the loss of the resulting film in theunexposed regions is increased. Therefore, the proportion of the acidcompound not falling within the defined range is unfavorable. In theresist composition of the present invention, the detail of the functionof the organic carboxylic acid compound is not clear at present.However, it is assumed that the organic carboxylic acid compound keepsthe delicate balance to the acid to be generated by exposure toradiations in the resist composition.

The positive resist composition of the present invention preferablycontains, in addition to the above-mentioned components, alight-absorbing agent so as to have a higher sensitivity and a higherresolution. As examples of the light-absorbing agent, mentioned aremercaptoxazole, mercaptobenzoxazole, merocaptoxazoline,mercaptobenzothiazole, benzoxazolinone, benzothiazolone,mercaptobenzoimidazole, urazole, thiouracil, mercaptopyrimidine,benzophenone and their derivatives. In particular, benzophenone ispreferred, since its ability to improve the sensitivity and theresolution of the composition containing it is excellent and since itadditionally has the ability to inhibit the influence of standing waveson the resist composition thereby making the composition not into resistpatterns with waved profiles but into resist patterns with truerectangular profiles. The proportion of the light-absorbing agent to bein the composition of the present invention may be not more than 30% byweight, preferably from 0.5 to 15% by weight, relative to the sum of thecomponents (A) and (B). If the proportion of the agent is more than 30%by weight, the profiles of the resist patterns to be given by thecomposition containing it are unfavorably worsened.

It is desirable that the positive resist composition of the presentinvention is used as a solution comprising the above-mentionedcomponents dissolved in a solvent. As examples of the solvent, mentionedare ketones such as acetone, methyl ethyl ketone, cyclohexanone, methylisoamyl ketone and 2-heptanone; polyhydric alcohols or derivativesthereof such as ethylene glycol, ethylene glycol monoacetate, diethyleneglycol, diethylene glycol monoacetate, propylene glycol, propyleneglycol monoacetate, dipropylene glycol, and dipropylene glycolmonoacetate as well as ethers thereof, for example monomethyl ethers,monoethyl ethers, monopropyl ethers, monobutyl ethers and monophenylethers; cyclic ethers such as dioxane; and esters such as methyllactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate,methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethylethoxy propionate, etc. These solvents can be used singly or as amixture of two or more of them.

The positive resist composition of the present invention may contain, ifdesired, conventional miscible additives, such as additional resins toimprove the properties of the resist films, as well as a plasticizer, astabilizer, a colorant, a surfactant, etc.

The positive resist composition of the present invention is dissolved ina solvent, and the resulting solution is coated on a substrate coatedwith an insulating film such as silicon nitride (SiN), BPSG or the likefilm or on a substrate coated with a metallic film such as titaniumnitride (TiN), Al--Si--Cu, tungsten or the like film, using a spinner orthe like, dried to form a photosensitive layer on said substrate,exposed to deep-UV rays, excimer laser beams via a desired mask patternor subjected to imaging with electron beams, using a minifyingprojection exposure machine or the like, and developed with a developersuch as a weakly-alkaline aqueous solution containing from 1 to 10% byweight of tetramethylammonium hydroxide or the like. After this process,a good resist pattern faithful to the mask pattern used is formed on thesubstrate, not depending on the kind of the substrate used.

Next, the present invention is described in more detail by means of thefollowing production examples and working examples, which, however, arenot intended to restrict the scope of the present invention.

PRODUCTION EXAMPLE 1

(Production of polyhydroxystyrene where 8 mol % of the hydroxyl groupshave been substituted by tert-butoxycarbonyl-oxy groups)

120 g of polyhydroxystyrene having a weight-average molecular weight of20,000 and a molecular weight distribution (M_(w) /M_(n)) of 4.0 weredissolved in 680 g of N,N-dimethyl acetamide, and 17.4 g ofdi-tert-butyl dicarbonate were added to the resulting solution andstirred to completely dissolve them. Next, 59 g of triethylamine weredropwise added thereto over a period of about 15 minutes with stillstirring. After the addition, this mixture was further stirred for about3 hours. Next, to the resulting solution added was pure water of 20times the solution. This was further stirred to make polyhydroxystyrenewhere the hydroxyl groups had been partly substituted bytert-butoxycarbonyloxy groups precipitated therein. Thethus-precipitated product was washed with pure water, dewatered anddried to obtain 125 g of polyhydroxystyrene where 8 mol % of thehydroxyl groups had been substituted by tert-butoxycarbonyloxy groups.

PRODUCTION EXAMPLE 2

(Production of polyhydroxystyrene where 35 mol % of the hydroxyl groupshave been substituted by tert-butoxycarbonyloxy groups)

145 g of polyhydroxystyrene where 35 mol % of the hydroxyl groups hadbeen substituted by tert-butoxy carbonyloxy groups were obtained as inthe same manner in Production Example 1, except that the added weight ofdi-tert-butyl di-carbonate was changed to 76.5 g.

PRODUCTION EXAMPLE 3

(Production of polyhydroxystyrene where 39 mol % of the hydroxyl groupshave been substituted by tert-butoxycarbonyloxy groups)

150 g of polyhydroxystyrene where 39 mol % of the hydroxyl groups hadbeen substituted by tert-butoxycarbonyloxy groups were obtained as inthe same manner in Production Example 1, except that the added weight ofdi-tert-butyldi-carbonate was changed to 85.0 g.

PRODUCTION EXAMPLE 4

(Production of polyhydroxystyrene where 70 mol % of the hydroxyl groupshave been substituted by tert-butoxycarbonyloxy groups)

180 g of polyhydroxystyrene where 70 mol % of the hydroxyl groups hadbeen substituted by tert-butoxycarbonyloxy groups were obtained as inthe same manner in Production Example 1, except that the added weight ofdi-tert-butyl dicarbonate was changed to 153 g.

PRODUCTION EXAMPLE 5

(Production of polyhydroxystyrene where 35 mol % of the hydroxyl groupshave been substituted by ethoxyethoxy groups)

120 g of polyhydroxystyrene having a weight-average molecular weight of20,000 and a molecular weight distribution (M_(w) /M_(n)) of 4.0 weredissolved in 680 g of N,N-dimethylacetamide, and 37.2 g of1-chloro-1-ethoxyethane were added to the resulting solution and stirredto completely dissolve them. Next, 78.8 g of triethylamine were dropwiseadded thereto over a period of about 30 minutes with still stirring.After the addition, this mixture was further stirred for about 3 hours.Next, to the resulting solution added was pure water of 20 times thesolution. This was further stirred. Thus, 130 g of polyhydroxystyrenewhere 35 mol % of the hydroxyl groups had been partly substituted by1-ethoxyethoxy groups were obtained.

PRODUCTION EXAMPLE 6

(Production of polyhydroxystyrene where 8 mol % of the hydroxyl groupshave been substituted by methoxy-n-propyloxy groups)

120 g of polyhydroxystyrene having a weight-average molecular weight of20,000 and a molecular weight distribution (M_(w) /M_(n)) of 4.0 weredissolved in 680 g of N,N-dimethylacetamide, and 8.6 g of1-chloro-1-methoxy-propane were added to the resulting solution andstirred to completely dissolve them. Next, 78.8 g of triethylamine weredropwise added thereto over a period of about 30 minutes with stillstirring. After the addition, this mixture was further stirred for about3 hours. Next, to the resulting solution added was pure water of 20times the solution. This was further stirred to make polyhydroxystyrenewhere the hydroxyl groups had been partly substituted by1-methoxy-n-propyloxy groups precipitated therein. The thus-precipitatedproduct was washed, dewatered and dried to obtain 125 g ofpolyhydroxystyrene where 8 mol % of the hydroxyl groups had beensubstituted by 1-methoxy-n-propyloxy groups.

PRODUCTION EXAMPLE 7

(Production of polyhydroxystyrene where 39 mol % of the hydroxyl groupshave been substituted by methoxy-n-propyloxy groups)

130 g of polyhydroxystyrene where 39 mol % of the hydroxyl groups hadbeen substituted by 1-methoxy-n-propyloxy groups were obtained in thesame manner as in Production Example 6, except that the added weight of1-chloro-1-methoxypropane was changed to 42.3 g.

PRODUCTION EXAMPLE 8

(Production of polyhydroxystyrene where 70 mol % of the hydroxyl groupshave been substituted by methoxy-n-propyloxy groups)

150 g of polyhydroxystyrene where 70 mol % of the hydroxyl groups hadbeen substituted by 1-methoxy-n-propyloxy groups were obtained in thesame manner as in Production Example 6, except that the added weight of1-chloro-1-methoxy propane was changed to 75.6 g.

EXAMPLE 1

1.48 g of polyhydroxystyrene obtained in Production Example 2, in which35 mol % of the hydroxyl groups had been substituted bytert-butoxycarbonyloxy groups, and 1.48 g of polyhydroxystyrene obtainedin Production Example 5, in which 35 mol % of the hydroxyl groups hadbeen substituted by ethoxyethoxy groups, were dissolved in 16.8 g ofpropylene glycol monomethyl ether acetate, and 0.148 g ofbis(cyclohexyl-sulfonyl)diazomethane and 0.093 g of benzophenone wereadded thereto and dissolved. The resulting solution was filtered througha 0.2 μm membrane filter to obtain a coating liquid of positive resist.

The thus-prepared coating liquid was coated on a 6 inches silicon wafer,using a spinner, and dried on a hot plate at 90° C. for 90 seconds toform a resist film having a thickness of 0.7 μm on the wafer. This wasexposed via a test chart mask, using a minifying projection exposuremachine, NSR-2005EX8A (produced by Nicon Co.), heated at 120° C. for 90seconds, then developed by puddling it in an aqueous solution of 2.38%by weight of tetramethylammonium hydroxide for 65 seconds, washed withwater for 30 seconds, and dried to form a resist pattern on the wafer.The resist pattern thus formed was a 0.21 μm line-and-space pattern. Thecross-sectional profile of the resist pattern was good and almostrectangular, though somewhat trapezoidal. The resist pattern was notinfluenced by standing waves. The minimum exposure amount, at which theresist coated was patterned into a large-area resist pattern detectablewith the naked eye while the surface of the substrate was exposed to beseen, (this is hereinafter simply referred to as "minimum exposureamount") was measured to be 7 mJ/cm². The heat resistance of the 0.5 μmline pattern formed from the resist was measured to be at 130° C. (Theheat resistance as referred to herein means the temperature at which thepattern formed begins to flow under heat.) Apart from this, the resistfilm coated on the wafer was exposed, then left as it was for 15 minutesand then heated at 120° C. for 90 seconds. This was processed in thesame manner as above. However, the crosssectional profile of the resistpattern thus formed was T-shaped, and the finest patterning limit of theresist was to give a 0.3 μm line-and-space pattern.

EXAMPLE 2

A resist pattern was formed in the same manner as in Example 1, exceptthat benzophenone was not added to the coating liquid of positiveresist. The resist pattern thus formed was a 0.21 μm line-and-spacepattern. The cross-sectional profile of the resist pattern was good andalmost rectangular, though somewhat waved but in a negligible degree forpractical use. The minimum exposure amount for the resist was measuredto be 6 mJ/cm². The heat resistance of the 0.5 μm line pattern formedfrom the resist was measured to be at 130° C.

Comparative Example 1

2.96 g of polyhydroxystyrene obtained in Production Example 2, in which35 mol % of the hydroxyl groups had been substituted bytert-butoxycarbonyloxy groups, were dissolved in 16.8 g of propyleneglycol monomethyl ether acetate, and 0.148 g ofbis(cyclohexylsulfonyl)diazomethane and 0.093 g of benzophenone wereadded thereto and dissolved. The resulting solution was filtered througha 0.2 μm membrane filter to obtain a coating liquid of positive resist.

Using the thus-prepared coating liquid, a resist pattern was formed inthe same manner as in Example 1. However, the finest patterning limit ofthe resist was to give a 0.28 μm line-and-space pattern. Thecrosssectional profile of the pattern thus formed was not good, as beingexpanded downward to the substrate. The minimum exposure amount for theresist was measured to be 35 mJ/cm². The heat resistance of the 0.5 μmline pattern formed from the resist was measured to be at 150° C.

Comparative Example 2

2.96 g of polyhydroxystyrene obtained in Production Example 5, in which35 mol % of the hydroxyl groups had been substituted by ethoxyethoxygroups, were dissolved in 16.8 g of propylene glycol monomethyl etheracetate, and 0.148 g of bis(cyclohexylsulfonyl)diazomethane and 0.093 gof benzophenone were added thereto and dissolved. The resulting solutionwas filtered through a 0.2 μm membrane filter to obtain a coating liquidof positive resist.

Using the thus-prepared coating liquid, a resist pattern was formed inthe same manner as in Example 1. However, the finest patterning limit ofthe resist was to give a 0.25 μm line-and-space pattern. Thecrosssectional profile of the pattern thus formed was not good, havingan inverted triangular shape. The minimum exposure amount for the resistwas measured to be 7 mJ/cm². The heat resistance of the 0.5 μm linepattern formed from the resist was measured to be at 120° C.

EXAMPLE 3

1.48 g of polyhydroxystyrene (having a weight-average molecular weightof 20,000 and a morecular weight distribution (M_(w) /M_(n)) of 4.0)obtained in Production Example 2, in which 35 mol % of the hydroxylgroups had been substituted by tert-butoxycarbonyloxy groups, and 1.48 gof polyhydroxystyrene (having a weight-average molecular weight of20,000 and a morecular weight distribution (M_(w) /M_(n)) of 4.0)obtained in Production Example 5, in which 35 mol % of the hydroxylgroups had been substituted by ethoxyethoxy groups, were dissolved in16.8 g of propylene glycol monomethyl ether acetate, and 0.148 g ofbis(cyclohexylsulfonyl)diazomethane, 0.093 g of benzophenone and 0.0032g of o-hydroxybenzoic acid were added thereto and dissolved. Theresulting solution was filtered through a 0.2 μm membrane filter toobtain a coating liquid of positive resist.

The thus-prepared coating liquid was coated on a 6 inches silicon wafer,using a spinner, and dried on a hot plate at 90° C. for 90 seconds toform a resist film having a thickness of 0.7 μm on the wafer. This wasexposed to excimer laser via a test chart mask, using a minifyingprojection exposure machine, NSR-2005EX8A (produced by Nicon Co.),heated at 120° C. for 90 seconds, then developed by puddling it in anaqueous solution of 2.38% by weight of tetramethylammonium hydroxide for65 seconds, washed with water for 30 seconds, and dried to form a resistpattern on the wafer. The resist pattern thus formed was a 0.21 μmline-and-space pattern. The crosssectional profile of the resist patternwas good and almost rectangular, though somewhat roundish at the top.The resist pattern was not influenced by standing waves. The minimumexposure amount was measured to be 7 mJ/cm². The heat resistance of the0.5 μm line pattern formed from the resist was measured to be at 130° C.The width of focus depth was evaluated based on a criteria that themaximum width (μm) of a focus by which a 0.25 μm line-and-space patternwas formed by 1:1 was 1.0 μm or more as "A" rank and the maximum widthwas less than 1.0 μm as "B", rank. As a result, the width of focus depthwas determined to be "A". When the resist solution was stored in a brownbottle at 250° C. for evaluation of storage stability, no generation ofsolid substances had been observed for six months.

Using this resist, a resist pattern was formed in the same manner asabove, except that the resist was, after exposed, left as it was for 15minutes and then heated at 120 for 90 seconds. The resist pattern thusformed was a 0.21 μm line-and-space pattern having a good, rectangularcross-sectional profile.

EXAMPLE 4

A resist pattern was formed in the same manner as in Example 3, exceptthat benzophenone was not added to the coating liquid of positive resistcomposition. The resist pattern thus formed was a 0.23 μm line-and-spacepattern. The crosssectional profile of the resist pattern was good andalmost rectangular, though somewhat roundish at the top and waved but ina negligible degree for practical use. The minimum exposure amount forthe resist was measured to be 8 mJ/cm². The heat resistance of the 0.5μm line pattern formed from the resist was measured to be at 130° C. Thewidth of focus depth was evaluated in the same manner as in Example 3 tobe "A" rank. In addition, when the storage stability of the resistsolution was evaluated in the same manner as in Example 3, no generationof solid substances had been observed for six months.

Using this resist, a resist pattern was formed in the same manner as inExample 3, except that the resist was, after exposed, left as it was for15 minutes and then heated at 120° C. for 90 seconds. The resist patternthus formed was a 0.23 μm line-and-space pattern having a goodcrosssectional profile.

EXAMPLE 5

A resist pattern was formed in the same manner as in Example 3, exceptthat 0.0062 g of SAX (trade name, produced by Mitsui Toatsu ChemicalCo.) which is sold as a phenolic compound, were used in place ofo-hydroxybenzoic acid. The resist pattern thus formed was a 0.21 μmline-and-space pattern. The crosssectional profile of the resist patternwas good and rectangular, without being influenced by standing waves.The minimum exposure amount for the resist was measured to be 7 mJ/cm².The heat resistance of the 0.5 μm line pattern formed from the resistwas measured to be at 130° C. The width of focus depth was evaluated inthe same manner as in Example 3 to be "A" rank. In addition, when thestorage stability of the resist solution was evaluated in the samemanner as in Example 3, no generation of solid substances had beenobserved for six months.

Using this resist, a resist pattern was formed in the same manner as inExample 3, except that the resist was, after exposed, left as it was for15 minutes and then heated at 120° C. for 90 seconds. The resist patternthus formed was a 0.21 μm line-and-space pattern having a good,rectangular crosssectional profile.

EXAMPLE 6

A resist pattern was formed in the same manner as in Example 3, exceptthat 0.0062 g of acrylic acid were used in place of o-hydroxybenzoicacid. The resist pattern thus formed was a 0.21 μm line-and-spacepattern. The cross-sectional profile of the resist pattern was good andrectangular, without being influenced by standing waves. The minimumexposure amount for the resist was measured to be 7 mJ/cm². The heatresistance of the 0.5 μm line pattern formed from the resist wasmeasured to be at 130° C. The width of focus depth was evaluated in thesame manner as in Example 3 to be "A" rank. In addition, when thestorage stability of the resist solution was evaluated in the samemanner as in Example 3, no generation of solid substances had beenobserved for six months.

Using this resist, a resist pattern was formed in the same manner as inExample 3, except that the resist was, after exposed, left as it was for15 minutes and then heated at 120° C. for 90 seconds. The resist patternthus formed was a 0.21 μm line-and-space pattern having a good,rectangular crosssectional profile.

EXAMPLE 7

1.05 g of polyhydroxystyrene obtained in Production Example 3, in which39 mol % of the hydroxyl groups had been substituted bytert-butoxycarbonyloxy groups, and 1.95 g of polyhydroxystyrene obtainedin Production Example 7, in which 39 mol % of the hydroxyl groups hadbeen substituted by 1-methoxy-n-propyloxy groups, were dissolved in 16.8g of propylene glycol monomethyl ether acetate, and 0.21 g ofbis(cyclohexylsulfonyl)diazomethane and 0.009 g of o-nitrobenzoic acidwere added thereto and dissolved. The resulting solution was filteredthrough a 0.2 μm memtbrane filter to obtain a coating liquid of positiveresist.

The thus-prepared coating liquid was coated on a 6 inches silicon wafer,using a spinner, and dried on a hot plate at 90° C. for 90 seconds toform a resist film having a thickness of 0.7 μm on the wafer. This wasexposed via a test chart mask, using a minifying projection exposuremachine, NSR-2005EX8A (produced by Nicon Co.), heated at 110° C. for 90seconds, then developed by puddling it in an aqueous solution of 2.38%by weight of tetramethylammonium hydroxide for 65 seconds, washed withwater for 30 seconds, and dried to form a resist pattern on the wafer.The resist pattern thus formed was a 0.22 μm line-and-space pattern. Thecross-sectional profile of the resist pattern was good and rectangular,though somewhat waved but in a negligible degree for practical use. Theminimum exposure amount was measured to be 15 mJ/cm². The heatresistance of the 0.5 μm line pattern formed from the resist wasmeasured to be at 130° C. The width of focus depth was evaluated in thesame manner as in Example 3 to be "A" rank. In addition, when thestorage stability of the resist solution was evaluated in the samemanner as in Example 3, no generation of solid substances had beenobserved for six months.

EXAMPLE 8

A coating liquid of resist was formed in the same manner as in Example7, except that SAX (trade name, produced by Mitsui Toatsu Chemical Co.)was used in place of o-nitrobenzoic acid and that 0.128 g ofbenzophenone were added to the liquid. The properties of the thus-formedresist were evaluated in the same manner as in Example 7. This resistgave a 0.22 μm line-and-space pattern. The crosssectional profile of theresist pattern thus formed was good and rectangular, without beinginfluenced by standing waves. The minimum exposure amount for the resistwas measured to be 13 mJ/cm². The heat resistance of the 0.5 μm linepattern formed from the resist was measured to be at 130° C. The widthof focus depth was evaluated in the same manner as in Example 3 to be"A" rank. In addition, when the storage stability of the resist solutionwas evaluated in the same manner as in Example 3, no generation of solidsubstances had been observed for six months.

EXAMPLE 9

A coating liquid of resist was formed in the same manner as in Example7, except that 0.003 g of o-hydroxy benzoic acid were used in place ofo-nitrobenzoic acid and 0. 128 g of benzophenone were then added.

The properties of the thus-formed resist were evaluated in the samemanner as in Example 7. This resist gave a 0.22 μm line-and-spacepattern. The cross-sectional profile of the resist pattern thus formedwas good and rectangular, although somewhat roundish at the top. Theresist pattern was not influenced by standing waves. The minimumexposure amount for the resist was measured to be 7 mJ/cm². The heatresistance of the 0.5 μm line pattern formed from the resist wasmeasured to be at 130° C. The width of focus depth was evaluated in thesame manner as in Example 3 to be "A" rank. In addition, when thestorage stability of the resist solution was evaluated in the samemanner as in Example 3, no generation of solid substances had beenobserved for six months.

EXAMPLE 10

A coating liquid of positive resist was formed in the same manner as inExample 7, except that 0.009 g of 1,1-cyclohexanedicarboxylic acid wereadded to the liquid in place of o-nitrobenzoic acid.

The properties of the thus-formed resist were evaluated in the samemanner as in Example 7. This resist gave a 0.21 μm line-and-spacepattern. The cross-sectional profile of the resist pattern thus formedwas good and rectangular, though somewhat waved but in a negligibledegree for practical use. The minimum exposure amount for the resist was13 mJ/cm². The heat resistance of the 0.5 μm line pattern formed fromthe resist was measured to be at 130° C. The width of focus depth wasevaluated in the same manner as in Example 3 to be "A" rank. Inaddition, when the storage stability of the resist solution wasevaluated in the same manner as in Example 3, no generation of solidsubstances had been observed for six months.

Using this resist, a resist pattern was formed as above, except that theresist was, after exposed, left as it was for 30 minutes and then heatedat 110° C. for 90 seconds. The resist pattern thus formed was a 0.21 μmline-and-space pattern having a good, rectangular crosssectionalprofile.

EXAMPLE 11

A coating liquid of positive resis was formed in the same manner as inExample 10, except that 0.12 g of benzophenone were then added to theliquid. The properties of the thus-formed resist were evaluated in thesame manner as in Example 10. This resist gave a 0.21 μm line-and-spacepattern. The crosssectional profile of the resist pattern was good andrectangular without being influenced by standing waves. The minimumexposure amount for the resist was measured to be 13 mJ/cm². The heatresistance of the 0.5 μm line pattern formed from the resist wasmeasured to be at 130° C. The width of focus depth was evaluated in thesame manner as in Example 3 to be "A" rank. In addition, when thestorage stability of the resist solution was evaluated in the samemanner as in Example 3, no generation of solid substances had beenobserved for six months.

The resist was, after exposed, left as it was for 30 minutes and thenheated at 110° C. for 90 seconds. The resist pattern thus formed was a0.21 μm line-and-space pattern having a good, rectangular crosssectionalprofile.

Comparative Example 3

1.05 g of polyhydroxystyrene obtained in Production Example 1, in which8% of the hydroxyl groups had been substituted by tert-butoxycarbonyloxygroups, and 1.95 g of polyhydroxystyrene obtained in Production Example6, in which 8% of the hydroxyl groups had been substituted bymethoxy-n-propyloxy groups, were dissolved in 16.8 g of propylene glycolmonomethyl ether acetate, and 0.21 g ofbis(cyclohexylsulfonyl)diazomethane, 0.009 g of o-nitrobenzoic acid and0. 128 g of benzophenone were added thereto and dissolved. The resultingsolution was filtered through a 0.2 μm membrane filter to obtain acoating liquid of positive resist.

The thus-prepared coating liquid was tried in the same manner as inExample 7 so as to evaluate the characteristics of the resist but invain, since this did not give a resist pattern.

Comparative Example 4

1.05 g of polyhydroxystyrene in Production Example 4, in which 70% ofthe hydroxyl groups had been substituted by tert-butoxycarbonyloxygroups, and 1.95 g of polyhydroxystyrene in Production Example 8, inwhich 70% of the hydroxyl groups had been substituted by1-methoxy-n-propyloxy groups, were dissolved in 16.8 g of propyleneglycol monomethyl ether acetate, and 0.21 g ofbis(cyclohexylsulfonyl)diazomethane, 0.009 g of SAX (trade name,produced by Mitsui Toatsu Chemical Co.) and 0.128 g of benzophenone wereadded thereto and dissolved. The resulting solution was filtered througha 0.2 μm membrane filter to obtain a coating liquid of positive resist.

The properties of the thus-formed resist were evaluated in the samemanner as in Example 7. The finest patterning limit of the resist was togive a 0.3 μm line-and-space pattern. The crosssectional profile of thepattern given by the resist was not good and T-shaped. The minimumexposure amount for the resist was 20 mJ/cm². The heat resistance of the0.5 μm line pattern formed from the resist was measured to be at 130° C.

Comparative Example 5

1.05 g of polyhydroxystyrene in Production Example 1, in which 8% of thehydroxyl groups had been substituted by tert-butoxycarbonyloxy groups,and 1.95 g of polyhydroxystyrene in Production Example 8, in which 70%of the hydroxyl groups had been substituted by 1-methoxy-n-propyloxygroups were dissolved in 16.8 g of propylene glycol monomethyletheracetate, and 0.21 g of bis(cyclohexylsulfonyl) diazomethane, 0.009 g ofphthalic acid and 0.128 g of benzophenone were added thereto anddissolved. The resulting solution was filtered through a 0.2 μm membranefilter to obtain a coating liquid of positive resist.

The properties of the thus-formed resist were evaluated in the samemanner as in Example 7. The finest patterning limit of the resist was togive a 0.3 μm line-and-space pattern. The crosssectional profile of thepattern given by the resist was not good, nearly having an invertedtriangular shape. The minimum exposure amount for the resist was 10mJ/cm². The heat resistance of the 0.5 μm line pattern formed from theresist was measured to be at 130° C.

Comparative Example 6

2.96 g of polyhydroxystyrene obtained in Production Example 2, in which35 mol % of the hydroxyl groups had been substituted bytert-butoxycarbonyloxy groups, was dissolved in 16.8 g of propyleneglycol monomethyl ether acetate, and 0.09 g of triphenylsulfoniumhexafluoroantimonate was added thereto and dissolved. The resultingsolution was filtered through a 0.2 μm membrane filter to obtain acoating liquid of positive resist.

Using the thus-prepared coating solution, a resit pattern was formed inthe same manner as in Example 1. However, the finest patterning limit ofthe resist was to give 0.30 μm line-and-space pattern. Thecrosssectional profile of the pattern thus formed was not good, beingbroadend upward. The minimum exposure amount for the resist was measuredto be 10 mJ/cm². The heat resistance of the 0.5 μm line pattern formedfrom the resist was measured to be at 140° C. The width of focus depthwas evaluted in the same manner as in Example 1 to be "B" rank.

The resist was, after exposed, left as it was for 15 minutes and thenheated at 120° C. for 90 seconds. The finest patterning limit of theresist was to give 0.5 μm line-and-space pattern. The crosssectionalprofile of the pattern thus formed was T-top shape.

EXAMPLE 12

A resist pattern was formed in the same manner as in Example 3, exceptthat a silicon wafer coated with an insulating film of silicon nitride(SiN) was used as the substrate.

The resist pattern thus formed was a 0.23 μm line-and-space pattern. Thecross-sectional profile of the resist pattern was good and almostrectangular, without being influenced by standing waves.

EXAMPLE 13

A resist pattern was formed in the same manner as in Example 3, exceptthat a silicon wafer coated with a metallic film of TiN was used as thesubstrate. The resist pattern thus formed was a 0.23 μm line-and-spacepattern. The cross-sectional profile of the resist pattern was good andalmost rectangular, without being influenced by standing waves.

EXAMPLE 14

A resist pattern was formed in the same manner as in Example 3, exceptthat a silicon wafer coated with an insulating film of BPSG was used asthe substrate. The resist pattern thus formed was a 0.23 μmline-and-space pattern. The crosssectional profile of the resist patternwas good and almost rectangular, without being influenced by standingwaves.

Comparative Example 7

A resist pattern was formed in the same manner as in Comparative Example6, except that a silicon wafer coated with a metallic film of SiN wasused as the substrate. The resist pattern thus formed was a 0.30 μmline-and-space pattern. The crosssectional profile of the resist patternwas expanded downward to the boundary between the pattern and thesubstrate.

Comparative Example 8

A resist pattern was formed in the same manner as in Example 1, exceptthat a silicon wafer coated with a insulating film of SiN was used asthe substrate. The crosssectional profile of the resist pattern wasexpanded downward.

EXAMPLE 15

0.9 g of polyhydroxystyrene obtained in Production Example 3, in which39 mol % of the hydroxyl groups had been substituted bytert-butoxycarbonyloxy groups, and 2.1 g of polyhydroxystyrene obtainedin Production Example 5, in which 35 mol % of the hydroxyl groups hadbeen substituted by ethoxy-ethoxy groups, were dissolved in 16.8 g ofpropylene glycol monomethyl ether acetate, and 0.15 g of pyrogalloltrimesylate and 6.3 mg of salicylic acid were added thereto anddissolved. The resulting solution was filtered through a 0.2 μm membranefilter to obtain a coating liquid of positive resist.

The thus-prepared coating liquid was coated on a 6 inches silicon wafer,using a spinner, and dried on a hot plate at 90° C. for 90 seconds toform a resist film having a thickness of 0.7 μm on the wafer. This wassubjected to imaging, using an electron beam radiator, HL-8000 (producedby Hitachi, Ltd.), heated at 110° C. for 90 seconds, then developed bypuddling it in an aqueous solution of 2.38% by weight oftetramethylammonium hydroxide for 65 seconds, washed with water for 30seconds, and dried to form a resist pattern on the wafer. In this way,0.12 μm contact holes were formed. The cross-sectional profile of theresist pattern thus formed was good and rectangular. The exposure amountfor this patterning was measured to be 25 μC/cm².

EXAMPLE 16

A coating liquid of positive resist was prepared in the same manner asin Example 15, except that 0.15 g of bis(p-tert-butylphenyl)iodoniumtrifluoromethanesulfonate were used as the acid-generating agent inplace of pyrogallol trimesylate.

Using this, a resist pattern was formed in the same manner as in Example15. 0.15 μm contact holes were formed. The cross-sectional profile ofthe resist pattern formed was good and rectangular. The exposure amountfor this patterning was 10 μC/cm².

EXAMPLE 17

A coating liquid of positive resist was prepared in the same manner asin Example 15, except that 0.15 g of 2,6-dinitrobenzylp-toluenesulfonate were used as the acid-generating agent in place ofpyrogallol trimesylate.

Using this, a resist pattern was formed in the same manner as in Example15. 0.14 μm contact holes were formed. The cross-sectional profile ofthe resist pattern formed was good and rectangular. The exposure amountfor this patterning was 35 μC/cm².

EXAMPLE 18

A coating liquid of positive resist was prepared in the same manner asin Example 15, except that 0.15 g of tri-phenylsulfoniumtrifluoromethanesulfonate were used as the acid-generating agent inplace of pyrogallol trimesylate.

Using this, a resist pattern was formed in the same manner as in Example15. 0.15 μm contact holes were formed. The cross-sectional profile ofthe resist pattern formed was good and rectangular. The exposure amountfor this patterning was 10 μC/cm².

EXAMPLE 19

0.9 g of polyhydroxystyrene obtained in Production Example 3, in which39 mol % of the hydroxyl groups had been substituted bytert-butoxycarbonyloxy groups, and 2.1 g of polyhydroxystyrene obtainedin Production Example 7, in which 39 mol % of the hydroxyl groups hadbeen substituted by 1-methoxy-n-propyloxy groups were dissolved in 16.8g of propylene glycol monomethylether acetate, and 0.03 g ofbis-(cyclohexylsulfonyl)diazomethane, and 0.15 g ofbis(2,4-dimethylphenylsulfonyl)diazomethane and 0.0064 g ofo-hydroxybenzoic acid were added thereto and dissolved. The resultingsolution was filtered through a 0.2 μm membrane filter to obtain acoating liquid of positive resist.

The properties of the thus-formed resist were evaluated in the samemanner as in Example 9. This resist gave a 0.2 μm line-and-spacepattern. The cross-sectional profile of the resist pattern thus formedwas good and rectangular though somewhat waved but in a negligibledegree for practical use. The minimum exposure amount for the resist wasmeasured to be 5 mJ/cm². The heat resistance of the 0.5 μm line-spacepattern formed from the resist was measured to be at 130° C. The widthof focus depth was evaluated in the same manner as in Example 3 to be"A" rank. In addition, when the storage stability of the resist solutionwas evaluated in the same manner as in Example 3, no generation of solidsubstances had been observed for six months.

What is claimed is:
 1. A positive resist composition comprising (A) aresin component whose solubility in an alkaline aqueous solution isincreased by the action of acids, and (B) a compound which generates anacid when exposed to radiations, wherein said resin component (A) is amixture comprising (a) a polyhydroxystyrene where from 10 to 60 mol % ofthe hydroxyl groups have been partly substituted by firstacid-releasable substituents, and (b) a polyhydroxystyrene where from 10to 60 mol % of the hydroxyl groups have been partly substituted bysecond acid-releasable substituents.
 2. The positive resist compositionaccording to claim 1, wherein said component (a) is a polyhydroxystyrenehaving hydroxyl groups partly substituted by first acid-releasablesubstituents which forms a resist pattern having an inverted triangularcross-section when patterned in the form of a positive resistcomposition containing said component (a) and said component (B), andsaid component (b) is a polyhydroxystyrene having hydroxyl groups partlysubstituted by second acid releasable substituents which forms a resistpattern having art expanded downward cross-section when patterned in theform of a positive resist composition containing said component (b) andsaid component (B).
 3. The positive resist composition according toclaim 1, wherein each of said components (a) and (b) has aweight-average molecular weight of from 8,000 to 22,000.
 4. The positiveresist composition according to claim 1, wherein said component (A) is amixture comprising, based on the total weight of said component (A),from 30 to 90% by weight of the component (a) and from 10 to 70% byweight of the component (b).